title: Multileaf collimation cardiac shielding in breast radiotherapy: Cardiac doses are reduced, but at what cost?
abstract: OBJECTIVE
  To measure cardiac tissue doses in left-sided breast cancer patients receiving supine tangential field radiotherapy with multileaf collimation (MLC) cardiac shielding of the heart and to assess the effect on target volume coverage.
  
  
  METHODS
  Sixty-seven consecutive patients who underwent adjuvant radiotherapy to the left breast (n = 48) or chest wall (n = 19) in 2009/2010 were analysed. The heart, left anterior descending coronary artery (LAD), whole breast and partial breast clinical target volumes (WBCTV and PBCTV) were outlined retrospectively (the latter only in patients who had undergone breast-conserving surgery [BCS]). The mean heart and LAD NTDmean and maximum LAD doses (LADmax) were calculated for all patients (NTDmean is a biologically weighted mean dose normalised to 2 Gy fractions using a standard linear quadratic model). Coverage of WBCTV and PBCTV by the 95% isodose was assessed (BCS patients only).
  
  
  RESULTS
  The mean heart NTDmean (standard deviation) was 0.8 (0.3) Gy, the mean LAD NTDmean 6.7 (4.3) Gy and the mean LADmax 40.3 (10.1) Gy. Coverage of the WBCTV by 95% isodose was <90% in one in three patients and PBCTV coverage <95% (range 78-94%) in one in 10 BCS patients.
  
  
  CONCLUSIONS
  The use of MLC cardiac shielding reduces doses to cardiac tissues at the expense of target tissue coverage. Formal target volume delineation in combination with an assessment of the likelihood of local relapse is recommended in order to aid decisions regarding field and MLC placement.
authors.affiliation: Department of Academic Radiotherapy, Royal Marsden NHS Foundation Trust, Sutton, UK. Electronic address: frederick.bartlett@rmh.nhs.uk.
authors.forename: F R
authors.initials: FR
authors.lastname: Bartlett
authors.forename: J R
authors.initials: JR
authors.lastname: Yarnold
authors.forename: E M
authors.initials: EM
authors.lastname: Donovan
authors.forename: P M
authors.initials: PM
authors.lastname: Evans
authors.forename: I
authors.initials: I
authors.lastname: Locke
authors.forename: A M
authors.initials: AM
authors.lastname: Kirby
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006321:Heart / Q000528:radiation effects*; D006801:Humans; D015412:Mastectomy, Segmental; D011832:Radiation Injuries / Q000517:prevention & control*; D011835:Radiation Protection / Q000295:instrumentation / Q000379:methods*; D015641:Radiography, Interventional; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant; D014057:Tomography, X-Ray Computed
keywords: Breast cancer; cardiac dose; cardiac shielding; radiotherapy; target tissue coverage